text:
How do young pilots in the USA accumulate 1500-hours to become a first officer?
The FAA requires 1500 hours as a pilot:

The rule requires first officers — also known as co-pilots — to hold an Airline Transport Pilot (ATP) certificate, requiring 1,500 hours total time as a pilot.

I am just interested in how can you get 1500 hours? This number is super huge unless you fly a trans-continental airliner. But you cannot fly an airliner without 1500 hours. Even having a private airplane, 1500 hours I assume will cost a lot - probably more than €500,000 in Europe. What is so specific about the USA? I fly gliders and a tug plane. I fly every weekend without exception and even sometimes after work. But I won't reach even 100 hours during the season. So to reach 1500 hours will take 20+ years. What about if you fly aerobatics...? Well of course there are some people who have these numbers but they are in their fifties and have spent all their lives in aviation! They don't even think about starting afresh in a first officer's career. So I am just curious how do young people log 1500 hours in the USA?

People were voting to close this question as 'unclear' so I added a link to what might be the FAA rule which you were asking about, and I changed the abbreviation "1500h" to "1500 hours", in case it was that that was unclear.

@ChrisW Haha, good, otherwise the answer would be "they just wait until 3p.m.!" ;-)

Another way to get your hours is to fly military, for the USAF or USN.

@PieterGeerkens -- military flying in general would do the trick, since it's a total-time requirement -- you could satisfy it with time in an Army UH-60.

@UnrecognizedFallingObject: Thank you; unintentional oversight to omit that possibility.

1 word: Instruction.
I learned to fly in the US, and all but one of the 10-15 instructors at the school were young guys who had a Commercial license and were just building hours while doing their exams and applying to airlines.
This meant they were actually getting paid (not particularly well, I hasten to add!) to build hours, rather than spending money on an airplane, or rental.
They say you don't become a pilot for the money, you do it because you love it. Nothing could be closer to the truth IMO.

I'm missing something here: FAA requires an ATP certificate. That requires 500 hours of multi-crew... how are people getting multi-crew hours while instructing on a SEP?

@Radu094 I suspect Instruction on SEP is not the only thing they're doing to get their requirements for ATP. But its certainly part of it.

@Radu094 can you point to the 500 hrs multi-crew experience requirement?  I'm not familiar with all the recent changes to the ATP requirements, but I can't seem to find that one in particular.

This makes it sound like accumulating your hours is a pyramid scheme!

Only if everyone's ultimate goal is ATP. It's not. Many people just fly for leisure.

There's a requirement for 500 cross-country hours on the new ATP, but no multi-crew experience requirement that I can find. There is, however, an upper limit of 500 hours on applicable time which can be applied to the total as a flight engineer.

Its 50 hours of multi-engine, not multi-crew (according to: https://www.faa.gov/news/press_releases/news_story.cfm?newsId=14838)

Hmm.. EASA's ATPL requires 500 h multi-crew. I somehow automatically misread the 500 cross-country as multi-crew. Strange that there is such a big difference in requirements between FAA ATP and EASA's ATPL

@Radu094 -- EASA also has the MCPL concept for new F/Os, which doesn't exist in the USA.

I think the most common answer will be, instructing. You'll build hours much faster doing that, since it sounds like you're only getting about 100 hours / year now, which isn't much.  Of course, the difference between a good instructor job and a bad one can be huge.
Other routes, which are not necessarily incompatible with instructing, would be things like traffic watch flying and banner tow.
At some point, most pilots probably start flying for somebody in a job that doesn't require ATP minimums -- night cargo, tour flying, etc. These jobs aren't entry level so they'll require some amount of experience, but not 1500 hours.
One pilot I know started doing right seat work at SimuFlight, filling the seat & reading the checklist for pilots who came in for the course without their own copilot. Eventually got an offer to start flying right seat for one of the pilots that came through for refresher training.  That's hardly common, but one-off stuff like that is out there.

Of course, the difference between a good instructor and a bad one can also be huge, and instructors who are doing it to build time rather than because they enjoy teaching can be bad ones.

@PeteBecker - I second that. As I mentioned above I learned to fly in this manner and was lucky enough to get a "good one". The bad ones were quite evident in their attitude.

But instructing doesn't work mathematically. It's not sustainable. One instructor can easily teach 5 instructors from 0 experience while collecting 1500 hours. What will other 4 do? We get 444*4... number of low hour instructors will grow like geometrical progression...

@Andrius You're assuming that the ones who are doing it for hours don't move on to other jobs (e.g. flying cargo or flying passengers) once they have enough hours. That's not a valid assumption. Also, teaching a single student from 0 hrs to CFI would be a lot of hours. Furthermore, most student pilots won't become CFIs, but will simply become private pilots who fly for fun (or else won't finish any pilot certificate at all, which is also quite common.)

No I assume that. 0 to CFI is about 230 hours. (1500 - 230(self))/230 = 5.5 You can take 0.5 for PPL as it's only 45h and losers. So we have 5. One is to replace after instructor leaves to airline 5-1 = 4. So 4 instructors nowhere to go.

@Andrius But the majority of pilots in the U.S. aren't intending to become ATPs. That's my point. It's not 1 out of 5, but rather something more like 9 out of 10 that aren't seeking their ATP and won't become instructors. Also, lots of private pilots will get an instrument rating and/or get instruction received time for other purposes, such as type ratings, so it's not just 40 hrs per PPL student. Further, some will get a commercial license (which requires 500 hrs, IIRC,) but not ATP or CFI.

Instructing is the most common route, however you can also fly as a commercial pilot in part 135 operations, which would be anything 30 seats or under charter, or 9 seats or less as a scheduled flight, and <= 7500 lbs payload. This link helps explain the differences. This would be small commuter airplanes, cargo, and air taxi operations. Also, experience does not have to come from US regulated air operations, you could go elsewhere in the world where the 1500 hour rule does not apply and get experience as a first officer and it should still count.

Note, that in USA there is a large pool of private pilots and therefore also competition for the pilot jobs. In Asia (both Middle East, India and Far East) airlines are growing, but there is almost no pool of private pilots there, so getting an entry level F/O job there might indeed be easier.

most people give the same scripted answer instruct, banner tow, part 91/135, cargo, skydivers etc.
but the reality is post covid measures era, short of networking or knowing an aircraft owner, your only 2 options is to instruct or pay for you time building hours. the kneejerk plus the excess of unemployed experienced pilots has made the 1st QTR 2021 difficult time for newly rated commercial pilots. part 135/91 carriers are demanding 1500 min for even a PC12 sic or Phenom 100 SIC. c208 1200hrs etc.


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Why are aircraft tyres not grooved horizontally?
Why are aircraft tyres not grooved horizontally like vehicle tyres? If the tyres are grooved horizontally won't it help in achieving more friction and reduce the chances of veering off?

horizontal grooves in tires has nothing to do with grip directly. They help in channeling water into the vertical grooves to avoid aquaplaning. They do increase rolling resistance which is detrimental to takeoff distance.

@ratchetfreak avoid aquaplanning at $V_1$ seems more important than rolling resistance  affecting take off distance in the event of a rejected takeoff on contaminated runway.

By the time you get to V1, the airfoils are going to be effective in controlling the aircraft.

@HowardMiller, at controlling yes, but the point is stopping the plane and most rejected take-offs won't be able to use thrust reversal (because the engine just failed).

Keep in mind, also, that runways with standing water (ie: puddles) deeper than 3mm are considered "contaminated" and special procedures (afaik) are required for such landings, where permitted. A wet runway should generally not have standing water, so extensive siping (or crosstreading) is not a prime requirement for water removal.  The bigger concern is lateral grip (aircraft can have large lateral loads due to crosswind conditions) and the more you groove a tread the more grip you sacrifice. I expect the tread design is grooved only as much as necessary to keep the contact patch area high.

@JanHudec: If you're rejecting due to an engine failure on a multiengine aircraft, you can still use reverse thrust on the other engine(s) - multiengine aircraft are required to be controllable with one engine failed and the other at full forward thrust, and full reverse thrust is only a small fraction of full forward thrust, so you won't lose control.

Almost all the aircraft operating from prepared surfaces have circumferential grooves in order to remove water between the tyre and runway surface.
From Dunlop site:

Most Dunlop aircraft tyre designs feature circumferential grooves moulded into the tread to disperse water from beneath the tread in wet runway conditions.
The tread helps to reduce the risk of aqua planing and improves traction and grip between the tread and runway surface.

In 1960s, NASA carried out a number of studies to determine the effect of tread design (among other things) for operating on wet runways and settled on the circumferential groove shape.
In case of aircraft operated from unpaved surfaces, the tyres may have some type of cross-tread pattern.

You have two questions here, lets just consider this for GA/commercial planes that are operated mainly from paved strips. Back country flying and grass/dirt strips lend to other tire needs.

Why are aircraft tyres not grooved horizontally like vehicle tyres?

Short answer, contrary to popular belief groves actually reduce grip. Vehicle tires are also designed to fit a different use case. Summer tires (mainly for dry times) can actually be close to aircraft tires in their cut (full slicks are not legal everywhere). All seasons are made to work well in not only rain but snow and ice as well. As such the groves are cut to displace water as well as provide limited traction on packed snow.

If the tyres are grooved horizontally won't it help in achieving more
  friction and reduce the chances of veering off?

No, but lets dig in. There are two cases to consider here, a wet runway and a dry runway. The coefficient of friction of rubber on dry asphalt is extremely high ~=.9 but when it comes to using tires to stop something (breaking really) you want the most rubber/asphalt contact you can get (also known as the contact patch). Thus the "grippiest" tire so to speak is whats commonly known as a racing slick since there are no groves. By adding tread you actually reduce grip by reducing the contact patch when talking about a dry runway.
Since airplanes sometimes operate in the wet (let's ignore snow), we need to account for that. To make a tire work well in the wet we need to displace the water so that the rubber can make contact with the asphalt. If you get a layer of water (even a thin film) between the tire and the asphalt you have what is commonly known as hydro planing (no, a seaplane rating won't check you out for this); you can read a full study on it here. Since you only need to provide area to displace the water to the simple groves provide enough space without adversely affecting grip as a traditinal car tread would.
Another somewhat related reason they may not be grooved laterally is to prevent the tires from spinning up which could cause other issues.
Older F1 Rain tires area actually cut very similar to aircraft tires as can be seen here

(source)
Compare to  this

(source)

I looked at that second image about 5 times and thought "why do grooved drag slicks even exist?" and "that's a funny looking dragster". Yeah, main landing gear. I get it now...

That F1 image is misleading: those tires do have cross-grooves, the exposure time is just too long to register them, see e.g. http://wpmedia.driving.ca/2014/03/97826821.jpg?quality=70&strip=all&w=960&h=480&crop=1

Thanks for the laugh at "a seaplane rating wont check you out for this".

It's certainly not universally true that all aircraft have length wise grooved tyres only.
Especially aircraft designed for use from rough and unprepared strips often have heavy duty tyres to deal with such conditions.
Think some military aircraft especially.
Here's an example of a Sea Fury deployed in Korea during the war there for example:
Linked from www.3rdattackgroup.com

Another example is the He-111:

Picture source. The link points to the full picture.

I can't help but notice that the Sea Fury has not just grooved tires, but what looks like two different styles of grooved tire.

@egid hadn't even noticed... Guess they fit what they have in combat, and what they had came off of another aircraft

This one may or may not have the original tires (at least they're both the same).

Runways have horizontal grooves on them to allow more surface area for water/slush to "hide" in. This feature helps keep the thickness of the fluid film low.
Most airplane tires avoid using horizontal geometric features—both blocks and sipes—so that the rubber on these wheels that land at around 250 km/h do not chunk out. At these high pressures the canals or ribs are enough to take care of hydroplaning. Horizontal ends further pose the disadvantage of groove wander if the pitches on the tires match that of the runway.
Moreover, airplane landing gears are designed strategically so that in the H configuration the front tires clear the track of slush for the rear pair to grip in.
Smaller aircraft and "off road" versions—typically small and light weight—have patterned tires. Some use these on the front alone while the rear tires that touch down first are simple rib tires.

Recently I came across a Wired article which mentions:

In the first moments after a plane touches down, the tires are skidding, not > rolling. The airplane essentially drags them down the runway until their rotational velocity matches the velocity of the plane. That's why they smoke upon landing, and why Michelin uses grooves instead of the block patterns seen on your car's rubber—blocks would simply break off. (Most tire wear comes from this moment of contact—where the rubber meets the runway.) The stoutest tires are rated for speeds of up to 288 mph.

Why are aircraft tires not grooved horizontally?
Because, unlike cars where the thrust is a force that acts on the drive wheels, in the point where they touch the ground, and has a forward orientation, the plane is pulled by propellers or pushed by jet engines and the wheels provide no thrust. So, horizontal grooves will not increase the thrust in the case of an aircraft. Even for trucks, the non drive wheels tend to have mainly vertical grooves with some minor horizontal cuts (see the picture).

Regarding "reducing the chances of veering off" the best grooves are the vertical ones because they can catch soil and increase the friction in case the plane tends to veer off course while trying to land. Horizontal grooves will have exactly the worst orientation, to the left and right, acting like skates for that direction.

Your first point is valid, however, braking force is applied through the wheels. (Reverse thrust cannot be counted on and is not figured into braking distance calculations.) As discussed in the other answers "veering off" is usually due to a hydroplaning on a wet surface - tires for unimproved runways do have a more "road car" like tread.

All of this is largely fundamentally wrong.  I would accept any credible evidence you have to support this, however.

The purpose of grooves in tyres is to disperse water, not to catch on roughness in the ground when the tyre starts to slide.

Grooves have also the role to disperse water (see: https://en.wikipedia.org/wiki/Tread) but the question is why the wheels of a plane possess only vertical grooves when having both vertical and horizontal seems a better option.

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What counts as "runway in sight" when flying an IFR approach to minimums?
I've watched a few videos on youtube where the pilot flies an Instrument Landing System (ILS) approach to the minimum allowed altitude before establishing visibility of the runway (MDA or minimums).
What I'm wondering though is what constitutes "runway in sight"?  I mean, in some cases that's going to be obvious (ie., you can see the runway clear as day long before minimums.)  But what if the cloud base is right at minimum and you can kind of see outside, but not in every direction (ie. maybe it's slightly clearer just a bit to your left than to your right.)
What do you have to see to consider the runway in sight?  The whole runway?  Just the lights? Just the approach lights?  Just the VASI/PAPI?  Would it be considered enough if, perhaps, you could see a windsock that you know is close to the runway?  Or perhaps there's a cross street right before the runway that you're very familiar with, would that work?  What would be considered "runway in sight" so that you can continue the approach rather than going missed?

Note/Clarification: The general rule, of course, is "when in doubt, go missed".  So in a lot of ways this question is academic.  What I would love, though, is a two part answer, with one part that has the exact rules (per the FAA) and the other with some common sense guidance on when to continue and when to go missed.

From FAR 91.175:

(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:
(i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.
(ii) The threshold.
(iii) The threshold markings.
(iv) The threshold lights.
(v) The runway end identifier lights.
(vi) The visual approach slope indicator.
(vii) The touchdown zone or touchdown zone markings.
(viii) The touchdown zone lights.
(ix) The runway or runway markings.
(x) The runway lights

Any chance you could expand on 91.175(3), I didn't know it could differ for Cat II and Cat III.

@JayCarr I think that that statement just means, Cat 2 + 3 have their own rules, don't use these general rules there. For Cat III, "fail operational" criteria & an Alert Height give a whole new set of "operations below DH" rules, or maybe the lack of a DH at all. Cat II rules that I'm familiar with aren't especially different from these, but are published in their own OpSpec, separate from Cat I rules.

Well, if you could just drop that explanation into your answer... that would go along way in making this answer correct.  Though I was hoping for some common sense guidance as well (if there is any to be had), about how much of any of the listed identifiers you need to see to really consider going.  It just feels like there are many things that could possibly be mistaken for things on that list.  I guess mostly what I'm asking for is "how certain is certain enough?"

On second look, our book says that the last two points (runway, its markings, its lights) are Cat I only. For Cat II or III it's necessary to have the touchdown zone of the runway or its markings or lights (or any of the other things) in sight. Seems like a strange case when you could see "the runway" but not "the touchdown zone" at 50' or 100', but that's the FAA for you. Why the VASI isn't similarly "Cat I Only" is entirely beyond me!

Huh, interesting...  But could you be persuaded into editing it into the answer?  The comments tend to disappear sometimes around here...

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What is the cause of tire marks at the extreme ends of runways?
At LAX, planes (usually) take off from east to west. On the west end of the runways there are dark tire marks.
What is the cause of thesey tire marks? Failed take offs? Late landings? Something else?

See Google Maps of LAX

Aircraft land in the same direction that they take off from, and you can see one aircraft in the image you posted heading out to that runway to take off. Which runway they choose depends on the wind (typically) so they will use whatever one favors a headwind.

The marks are left by the tires of landing planes when they touch down -- that is, ordinary routine landings.
The wheels of a landing aircraft do not start rotating before they hit the runway -- so right at the moment of touchdown, the wheels will at first skid along the runway surface until the friction between tires and runway has delivered enough angular momentum to the tire to spin it up so it matches the ground speed of the landing plane. Once that happens, the wheel will roll normally.
This skidding causes the skid marks you have observed.
Even if the runway is usually used in the east-to-west direction, there are still enough days where landings are from the west that both ends of the runway will collect tire marks. How many days that are doesn't really influence how black the runway gets, only how long it can go between having the rubber buildup cleaned off.
At the few airports that are really only used in one direction (such as the famous Princess Juliana Intl Airport at St. Maarten, which does not even have charted approaches from the east due to terrain obstacles) you will find the tire marks only at the touchdown end of the runway.

Seems logical enough. I was confused because I watch planes landing their all day from the east. Thanks for answering!

@Trevor When your Santa Ana winds https://en.wikipedia.org/wiki/Santa_Ana_winds blow from the east the planes land on that runway.  Yes it is not the typical direction for landing but happens often enough where you live.

Besides atypical weather, LAX prefers to land planes in this direction overnight as well (allows the approach to be over the ocean, reducing noise).  So it's used a lot when you're not necessarily watching.  https://www.lawa.org/uploadedFiles/LAX/noise/PDF/Final%20LAX%20Preferential%20Runway%20Use%20Policy%20Report%20041114_Web.pdf

That would be caused by the tires which are not rolling start rubbing away on the runway on touchdown. Since the tires are not moving, it is going to "scrape" on the runway and leave a mark. This problem is addressed by this question. It also produces some smoke as you can see in the image.

Image Source
Same thing happens when a car spins on the road.

I can't find the source for this.

+1 for the car doing donuts gif

Not just "the car", @AdityaSharma, but "the Lamborghini'!

The reason for the marks is that this is the touchdown zone of the runway. The aiming point for landing is the 1,000' marker, the pair of solid white stripes. This is where the ILS glideslope and visual landing aids are aligned. Planes to float past the touchdown marker because of the flair at the end of landing so the densest tire marks tend to be at and just beyond the marker.


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Southwest corner of LAX has peculiar airplane parts, what is this area?
In the Southwest corner of LAX (at the intersection of Imperial Highway and Pershing Dr.) there is a strange looking area that appears to have some abandoned airplane parts. Also, it looks like a road-striper had a good time one day doing donuts around one of the artifacts. Anyone familiar with this area and what it is used for?

See Google Maps

Great answers - any insights on the yellow lines?

It looks like the lines are just practicing/testing for painting taxiway and runway markings.

From the question title I thought you meant the corner where Southwest's terminal is located. Upon looking at the map I learned that Southwest's terminal is actually located in the north east corner of the airport. I don't know why but that made me laugh.

Maybe to avoid disposing of unused paint they just dump it there. Or they were a little excited about the next NASCAR race and had their own.

Related: LAFD Live Fire Training At LAX

All major airports have practice fire fighting facilities equipped with dummy aircraft that are made of steel so they don't burn.
In addition to the dummy steel aircraft, they will often use retired aircraft to use for familiarization and evacuation training.

Source

Source

Source

It is an aircraft fire simulator. They use it for training emergency response personnel and vehicles.
You can see them training on one in this YouTube video

Source: Leipzig Halle Airport

That confirms what I was going to post as a speculative comment. I got too busy playing around in the "3D" view and looking around the airport to come back to post...

Any idea what the "donut stripes" are in the OP's picture, though?

@yshavit I'm assuming like the other commentor on the OP that they test the stripe painting equipment and/or paint in that area.


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Under what circumstances are passengers boarded onto buses at gates A10 and A4 at Heathrow Terminal 5?
In Why doesn't Heathrow T5 have stand 504? it was suggested that gates A4 and A10 are so-called "bus-gates" where passengers board a bus to get to the aircraft.
Under what circumstances would passengers in Terminal 5A board a bus to get to the aircraft?
I can think of two instances:

Aircraft is parked South of taxiway Y, or
Aircraft is parked on remote stands East of taxiway D.

Are these correct, and are there other reasons this would happen?

Seems to be more of a pax question more suitable for [travel.se] than [aviation.se].

'Bus-ing stands' allow passengers to reach aircraft that are parked on 'remote' gates.
Not all stands have passenger jetties or air-bridges that connect to the terminal buildings.
Some stands are 'remote' because it allows for extra rows of parking spaces, without having to build additional terminal buildings, for example gates 524 to 527 which don't connect to terminal 'A'.
Also, jetties aren't long enough to reach the furthest stands 531 & 541 on terminal 'B'.  And the same goes for stands 551, 558, 567 & 568 on terminal 'C'.  (Although 561 does have a jetty, and it always seems like it might be the longest jetty in the world!!)
There is also an 'imaginary' terminal 'D' at Heathrow that hasn't been built, next to the fire station. Terminal 'D' allows for stands numbering in the 570's, 580's and 590's.  All of these require a bus to reach them.
Finally, stands 504 and 510 are 'missing'.  There are a few reasons I can think of for this:

They can be used to get passengers onto buses.
They allow stands 505, 508 & 512 to be larger, to park larger aircraft.
They allow stands 505 & 512 to be 'Muster' stands, so that passengers can be directed there safely in case of a terminal fire/evacuation.

Wow cool, I hope I get to walk on the 561 jetty one day! Thanks

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text:
Can you request a new squawk code if you don’t like the one being assigned?
Just out of curiosity. If you get assigned a squawk code and you don’t like it out of superstition or other negative associations you have with it, can you request a new one?

Tom, I want to publicly apologize for failing to support you. I was weak and wrong, as was everyone else who belittled you for your beliefs.

I was indeed given 4666 once. After my lengthy clearance readback, the controller said, "Umm, I can give you a new code if you like". But I told him, "Nope, actually, that one suits me just fine, thanks."

No, there is no procedure for assigning a new squawk code because a pilot is superstitious. The whole system behind assigning squawk codes is fairly complex, and requesting new codes for non-operational reasons would put extra load on the system for no reason. In many cases, the controller doesn't even have the option to manually change the code, and doing so could result in significantly increased workload (actually getting the code, updating the flight data record, communicationg with the pilot, coordinating with downstream sectors etc.).
Squawk codes are a limited resources, we only have 4096 of them, and the system is already near its limit in busy airspaces. If we started to change codes just because we feel like it, we may very well run out of codes. And how should we choose which codes to avoid? Some probably wouldn't like codes such as 4666, others 1313. What about a pilot not liking 2403 because it happens to be the date a relative of his died? 4 is an unlucky number in Chinese culture, should we avoid all squawk codes with 4 in them?
We use numbers in aviation for all sorts of things, all the time, and it simple does not make sense to avoid some of them for non-operational reasons.

Agreed. At the end of the day squawk code is just a number for ATC to identify us and keep us safe. I guess we will be better off focus on the flight itself than worried about superstitious factor.
But sometimes it’s just kind of interesting to have your own quirk and habit to keep yourself in piece of mind.

There are at least three reserved codes, right? So only 4093 available?

@RossPresser emergency codes are one thing, I suppose all-zeros would also be avoided.

@RossPresser There are several diferent codes that are reserved for specific purposes, some globally, some regionally. Either way, the total number of potentially available codes is 4096

Yeah, if you could request codes that would take a whole bunch out in China because they don't like 4.

Just in case someone wonders why 4 digits don't make up for 10,000 possible squawk codes: it is actually an octal number so the allowed digits are just 0-7 ($7777_8 = 4095_{10}$ being the max. code).

You can request a new one, but it’s up to ATC to decide whether to change it. Some will and some won’t, but mostly it depends on how busy they are.
I’ve seen discussions (in a private forum) about the specific case of pilots unhappy with 666, and a few controllers reported having gone out of their way to find a new squawk code that also had 666 in it. Others reported that they just change it themselves as soon as they see it. But the majority didn’t care either way.

Agreed, don’t think I want to add some extra workload to the ATC when they are already busy just because some number.

That won't work for most controllers who assign codes from some range and typically the first number, but often enough also the second number, is fixed depending on the airspace assigning or other variables concerning the flight.

@VladimirF My understanding is that is for what the computer automatically assigns, but they can try manually assigning one and the computer will allow it if the code isn’t already in use.

@StephenS But then the system must also respect ranges allocated for local traffic in various regions in the vicinity and ranges that are to be  given in the neighbouring FIRs. But everything is getting centralized now, EUROCONTROL has a common system for many countries now (not all of them) so perhaps it can be done.

A couple of times I have heard requests for change and they have been granted.  Several years ago I asked a couple of approach controllers about it.  The supervisor said that he simply avoids numbers with "666" because he is aware of pilot concerns.
In the days of codes being entered by dial switches, it happened, but was not common that there might be a sticky bit on the switch.  One plane I flew had that with the 0400 bit.  Fortunately, it rarely happened that a code was assigned with that bit.  If one was assigned, spinning the knob a few times might get it to work.
Normally the controller only has blocks, which at best, are the last two digits of the code.  So their ability to change codes is limited.
So I can't tell you the rules, cite the controller handbook, or provide a copy of a procedure, but I will say that it has been done, I have heard requests for different codes and I have heard the controller accommodate the request.

What’s the problem with 666 though? We usually assign 666x codes in my area but why shouldn’t pilot want those codes?

@pcfreakxx https://en.wikipedia.org/wiki/Number_of_the_beast

@AakashM I won‘t accept this as reason for a different squawk...

Well you can always ask...
ATC is unlikely to give you a requested code or change your code though. There are a few ways to get a code, either from an IFR flight plan submission, or from a local block(s) the associated controller uses for various things. How they are assigned is discussed here and the most recent beacon allocation plan can be found here. I cant say I have ever heard of it happening nor was i taught any such procedure in my flight training.

Sometimes it’s more scary to talk in a super busy radio frequency than 666 to me

Yes, you can. "Center, N123DY request a new squawk." There should be no problem with being issued a new one. The "06" subset is one of Denver Center's enroute squawks, so 0666 gets assigned pretty much every day. I've reissued squawks for that code on several occasions. It's not a big deal.
Fulfilling your request for a code consists of my pushing a button, entering your aircraft ID (which we have a 3-digit shortcut for), and reading the new beacon out to you.

This is for the Enroute environment. It is not that simple in the Terminal environment, and even less so if you're on a NAS code (flight following or IFR flight plan) instead of a local code.

Well, in the Center environment, we did it all the time. I've never read Chapter 3, though, or any of that stuff that says "Terminal" .  :)
As far as a NAS code goes, it takes , as I said, a button push, a CID, and enter.

I'm not disputing your account of what you have to do, just letting people know that it's not as simple as all that for some of us.

Yeah, no problem. Come on out to Longmont, lunch is on me.

authors: Vladimir F Героям слава


text:
Why does Schiphol airport have such a long taxi way?
I heard that from runway 18R-36L the taxi time is around 20 minutes, I heard that this runway was built and is used mainly to reduce noise pollution, but what reasons are there for the length of the taxi?

Unanswerable unless you can put an exact dollar value on noise reduction, people's time, and jet fuel (hint: it's only possible for one of them).

The answer is a matter of opinion. Those who place a greater premium on less noise would argue it is worth the extra fuel. Those who don't would say it's not.

I can understand that people living near airports want to reduce noise, but does it worth the amount of fuel the airplane burns and the extra CO2 emissions.

@pedrogalindez I bet if you went around the area and said "would you rather have loud aircraft around your house 18-24 hours a day, or have them burn an extra 10 minutes of jet fuel, what would you want?" Almost all of them would say that they want them to spend the extra fuel. Noise problems have closed airports and airports don't want to tick off the neighbors, so a little extra taxiing is better than an angry mob of local homeowners.

Noise does not seem to be as much a consideration as available space is. The runway was built after the highway system surrounding the airport.

Q: "Why is the railway station so far from the town?" A: "To be close to the railway." The question here is incorrect. It should be, "Why was the runway built so far from the passenger terminal?"

"Why is the taxi time 20 minutes?" Because the taxiway is long. "Why is the taxiway long?" Because the runway is far away. "Why is the runway far away?" To reduce noise pollution by moving it further into a rural area, in EHAM's case. It makes more sense than building a new major airport further out in the country.

Firstly, I'd like to make clear that the particular reasons for the placement of the taxiway are not all publicly disclosed, and there are undoubtably multiple factors involved. After looking at the airport in Google Maps, I notice a couple things. (Excuse the large picture, explanation below!)

1) Physical & Geographical Limitations
There is a pre-existing highway in between the runway and the rest of the airport. The runway could not be placed closer to the airport in the current direction without either removing the highway, or bridging over the highway (as the taxiway does). The highway would be unlikely to ever be removed, due to the extreme cost of removing pre-existing infrastructure, nor would they like to bridge a runway over the highway. Runways require a fair amount of maintenance in comparison to taxiways, and including a bridge in the design of said runway would drastically increase the cost and complexity of maintenance.
Looking at the map, there is absolutely nowhere to place a runway of that length and bearing without drastically engineering a solution. Beyond that, there does not seem to be anywhere within the "block" of the main airport to create a runway of that size, regardless of bearing.

2) Noise Abatement
The fact that the runway is in a less dense area also means that aircraft on approach would cause less noise disturbance for the populated areas nearer the core of the airport. In fact, for the northern approach, there are not many developed areas - it is primarily open fields. Aircraft are only allowed to takeoff to the north, and land from the north, on this runway, to avoid overflying the populated areas to the south of it.

3) Other Potential Factors
The above reasoning we can be relatively certain about. However, there may be other contributing factors, such as ground quality. As there are rivers and streams nearby (including the one that the taxiway bridges), much of the ground may be more difficult to build on, and require more expansive foundations.

Conclusion
Regarding a taxi time of twenty minutes, there is certainly potential for a taxi of that length, but it is not due to distance. The distance is not anything extraordinary compared to many other "Hub" airports. The time is likely substantially increased by the fact that, if runway 18/36 is in use, they will likely be told to taxi around 18/36. The primary reasons for the creation of this runway, cited by the planning committee, were arrival/departure capacity and noise abatement.
While this is certainly not a very efficient system, it is certainly the only solution I can see to provide a runway of that size. There could be various improvements, but cost is the overarching factor.

"including a bridge in the design of said runway would drastically increase the cost and complexity of maintenance" it might, but if you look at the east end of 09/27, you'll notice that it bridges over the E19/A4. Not only that, but the aiming marks are directly on the bridge which means that aircraft land there sometimes.

@FreeMan The A4 tunnels under 09/27 rather than the runway "bridging" over. You can see the terrain and the runway stay level.Presumably the runway does not rest directly on the roof of the tunnel, but there is bit of earth separation between. This puts the cost primarily on the highway operators, rather than the runway operators.  It does not require much additional engineering in this fashion for the runway, while creating a bridge over the river and highway would require more engineering.

Not quite sure I follow you, @Matt. I would expect any road/aircraft interchange to involve the roadway going under the taxi-/run-way. While local soil conditions could make it it more difficult/expensive, I see no obvious reason (based on 30 seconds of scanning the aerial view on Google Maps - an obviously rigorous methodology ;)  that the same type of grade separated crossing couldn't have been made for Rwy 18/36 and the N520. Thus shortening the taxi times and honking off the local residents who would have been displaced.

@FreeMan If you zoom in on the highway, it has a river inbetween. This makes tunnelling much more difficult and costly, as they will have to hold back, or potentially redirect, the water. In the 3D view of the taxiway bridge, you can see that it is not very thick, which would not be sufficient for a load/force bearing runway.

@FreeMan Here is an image of the underside of the bridge: https://i.imgur.com/3wOTkeg.jpg

The A7 was in planning when the decision was made to place the 36L where it is, so that's not a factor. The N520 you are correct about, it's been there for decades, but could have been put through a tunnel under the runway, as has been done with the A4 and railway lines near the airport. The main reason (as far as I'm aware) is actually the ability to purchase or otherwise acquire the needed land to build the runway.

@Matt while not a runway, there's also a bridge over the A4 for one of the main taxiways, which has been there for decades and is actually a reporting point for aircraft, which will notify ATC they are "over the bridge".

@jwenting Aye, but there are different structural requirements for taxiways. There's different regulations we have to comply to when laying runways rather than taxiways.

@jwenting Regarding planning on the A4, it's dependent upon what stage it is in. Highway planning is a multi-million dollar project - I have friends that have made it a full time career! If the plans are already underway, and the runway comes in as an afterthought, they are not likely to change it without considerable reasons.

It's not unheard of for a highway to tunnel under an active runway. See for instance runway 2C and taxiway S at KBNA.

@MichaelHampton Please read full conversation for context. Certainly highways go under runways. However at KBNA the tunnel is deeper, and there is a fair amount of separation between tunnel ceiling and runway foundation. With this airport, as I said, tunneling along a river is a fair bit more difficult.

Also Rwy 10/28 at KATL

@Matt The A4 was planned at the same time as the runway, roughly. Or rather the widening of he old N4 (2 or 4 lane) highway into the A4 (8 lane) freeway was done in tandem with the airport expansion.


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What are the specific side step minimums for an approach?
This question piques my curiosity a bit on this subject.  In regards to circling approaches the AIM 5-4-19 states that

a. ATC may authorize a standard instrument approach procedure which serves either one of parallel runways that are separated by 1,200 feet or less followed by a straight-in landing on the adjacent runway.
b. Aircraft that will execute a side-step maneuver will be cleared for a specified approach procedure and landing on the adjacent parallel runway. Example, “cleared ILS runway 7 left approach, side-step to runway 7 right.” Pilots are expected to commence the side-step maneuver as soon as possible after the runway or runway environment is in sight. Compliance with minimum altitudes associated with stepdown fixes is expected even after the side-step maneuver is initiated.
Note: Side-step minima are flown to a Minimum Descent Altitude (MDA) regardless of the approach authorized.
c. Landing minimums to the adjacent runway will be based on nonprecision criteria and therefore higher than the precision minimums to the primary runway, but will normally be lower than the published circling minimums.

However I’m not aware of any approach plates which list specific side step minimums on them for airports with parallel runways where sidestepping is commonly used.  Examples below are from Boeing Field in Seattle, WA, and John Wayne in Santa Ana, CA.

So my question here is as the plates do not specifically publish a side step set of minimums, should the approaches be flown down to the localizer MDAs or use the Circling MDAs?  Is this up to a pilot’s preference or is it a matter of just how far away the landing runway is from the parallel approach runway?

KSFO has sidestep minima for ILS/LOC 28R to 28L but not from ILS/LOC 28L to 28R.  It also has a sidestep from ILS/LOC 19L to 19R but no ILS at all for 19R itself.  The latter is probably the more normal case for sidesteps: giving a second runway (probably one normally only used for departures) lower minima than circling without needing to install and maintain another entire ILS setup that would rarely be used.  Notice that the first two also have (much higher) circling minima.
KDFW has sidestep minima for ILS/LOC 35L to 35C, ILS/LOC 35C to 35L, ILS/LOC 36L to 36R, ILS/LOC 36R to 36L, and all their opposites.  Since all the sidestep targets have an ILS of their own, this seems to be intended only for when one of them is out of service, i.e. not for normal usage.


text:
Has there ever been an aircraft with three sets of flight controls?
On every aircraft I know, there is either one set of flight controls if it is single-pilot operated, or two sets of flight controls allowing either the pilot or copilot full control.
Has there ever been an aircraft that has three or more sets of flight controls?
To clarify:

"aircraft" includes fixed-wing, helicopter, powered lift etc.
remotely operated aircraft do not count.
A set of flight controls consists of yokes, pedals and/or sticks that allow the operator to manipulate the pitch, roll and yaw axes.

You could say most WWII bombers had a third set of controls for the bombardier. On the bombing run control of the aircraft was turned over to the bomb sight. I don't know if it controlled all axes, though, or how much control authority it had, since it was intended for fine adjustments

Dave's second reference (here) includes two helicopters with a third set of controls:
The Boeing BV-347 (link)

Sikorsky S-64 (link) and it's predecessor the S-60

a retractable gondola which was fitted within the helicopter's fuselage. This compartment was equipped with a set of flight controls and could be lowered down allowing a third pilot to fly the aircraft while facing towards the rear! Is that the rickety shed-cum-greenhouse hanging just forward of the front wheels? Everything about it, that it came from B&Q with a free tomato plant, the fact it'll be crushed if you land, the fact it faces backwards, is All Awesome.

Are you sure it's not just something in the background?  I think I see the words "Police box"...

The Sky Crane's third pilot does not Have rudder pedals so technically they do not have "full control", but it is close.

Depends if you are asking about production or testbed stuff, NASA had at least one test bed aircraft that looks to have had at least 4 sets of controls (also covered in this question).
If you consider the space shuttle an aircraft, some of the thrusting capabilities (enough for pitch roll and yaw I belive) were operable from the arm control position.

Rotation and translation were both available from the aft station on shuttle -- it was how they did docking, since the docking adapter was in the payload bay.  Interestingly, the translational hand controllers didn't look like that diagram indicates.  They looked like this (the far left of the front panel, the stick with the square head): http://www.collectspace.com/images/news-062611a/013.jpg


text:
What are the chances that you are on plane that has an incident?
ICAO Annex 13 defines an "incident" as

An occurrence, other than an accident, associated with the operation of an aircraft which affects or could affect the safety of operation.

Is there good record keeping about incidents globally? Not like Aviation Global Incident Map which only really only lists accidents and some airport issues.
For completeness, the same document defines an "accident" to be

An occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight until such time as all such persons have disembarked, in which (a) a person is fatally or seriously injured [...], (b) the aircraft sustains damage or structural failure [...] or (c) the aircraft is missing or is completely inaccessible.

Only incidents that an airliner pilot is aware mid-flight and can do something about -this a start to follow-up.  question. Exact likelihood is not important- is it 10% or 20%. For passengers, the likelihood is not important since pilots handle mainly well.

This is very difficult to answer because your definition of incident is quite vague. What is standard flying? Is a go around, instructed by Air Traffic Control because the runway is occupied, standard flying? Or when the go around was decided by the flight crew because the approach was unstable? Is an inoperative auto-thrust system, which results in manual thrust setting throughout the flight, standard flying? And if it fails in flight?

There is avherald.com but it doesn't record all incidents

although accident is quite simple to define (let's say "at least one casualty"), incident is not. For your car, do you consider a failure in windscreen wiper on a sunny day as an incident?

@ManuH "Accident" is defined by Annex 13 of the Convention on International Civil Aviation: we don't need to make up our own definition.

@DeltaLima I've removed the vagueness by inserting the ICAO definition of "incident".

The chance of any given passenger being involved in an incident is is both approximately zero, and also far less than the chance of being involved in an incident getting to-and-from the airport or just walking through the terminal.

Define yourself more precisely please. Is the question about "major injuries" or "fatalities", then you can ask precisely how many fatalities do you have per 10^9 miles or per 10^6 flights or similar. The number is very low. Also, it depends on the type of plane. If you consider military flights (including missions), the rate is orders of magnitude higher.

@DavidRicherby "incident" is still vaguely (or at least very broadly) defined. If a pilot has a sneezing fit that could meet the ICAO definition of incident (it could affect the safety of operation as they can't very well safely operate a plane if I'm having a sneezing fit, can they? Further in a two-person crew operation it could significantly distract the other pilot...)

Regardless of your definition of "incident", there are quite simply too many factors in play. The type of the aircraft, the pilots, the region you're flying from/to, etc... all play a role in what "incidents" may happen and how likely they are to happen. Unfortunately, there isn't some blanket statement we can make in this area, although you can feel free to make your own judgement based off historic data.

This can't really be answered because many incidents are only identified long after the fact (eg. a recent report on a problem with a Jetconnect B737, where the actual incident took place sometime between when the aircraft was assembled in 2011, and when the damage was found in 2013).  For that matter, many incidents are never identified.

I'm voting to leave closed for basically the reasons that bluefish states: Any answer will depend way too much on other factors (not the least of these being the pilot(s) [including experience,] aircraft type, location, maintenance, airline, and weather.)

@DavidRicherby my point is that incident is difficult to define althought it is quite easy to agree on a definition of accident. I didn't know there was already a definition somewhere. I link the convention.

I see you've edited the question to try to be more on-topic. You might find it is easier to be on-topic by rewording the question as "how many incidents are there annually", or something along those lines. You can then compare that to the number of flights annually.

I don't know if there is a global compilation. But for Australian operations data exists to allow us to establish a likelihood of being in an incident. Accidents are so rare that it's difficult to get a reliable indicator, however if we are just measuring reported incidents I believe we could get somewhere.
The Australian Transport Safety Bureau (ATSB) has published an "Aviation Occurrence Statistics" report covering 2004-2013.
Let's focus on high-capacity RPT operations, because lets face it, that is probably what most people are interested in.
According to the report, in 2013, there were 597,000 departures of Australian-registered high capacity RPT or charter flights (unfortunately the report doesn't seem to split it into RPT only, possibly because we have a lot of high-capacity charter flights to the mines). In the same year there were 3292 reported incidents to the ATSB and 2 accidents. Therefore I would conclude that if in 2013 you boarded an Australian-registered high-capacity RPT or charter flight, your chances of being in a reported incident were around 0.5%, and chances of being are an accident is 0.06%. The incident percentage is approximately the same for the couple of years prior, so I am confident that this remains around about the mark today - though I would not consider the accident rate to be reliable because there were so few.
The incidents cited in this data vary from loss of separation to a pilot being sick to birdstrikes.
Have a read of the report but before you take it as gospel, keep in mind, as they say, "there are lies, damn lies, and statistics!"


text:
What was the story of a serious incident with Galaxy C5 in about 1973

I am guessing it was a flight in support of the Yom Kippur War in October of 1973 that due a pitot tube failure that Galaxy C5 had to do an emergency landing on Azore with assitance from another plane but finding any details about it spoiled by the higher profile Vietnam War Babylift operation major incident. What caused its pitot tube to fail? The video isn't an accident investigation. It only says their pitot tube failed and they didn't have altitude or speed readings.

I don't have the opportunity to watch the video right now, but what is it about the incident that the video doesn't explain to your satisfaction? Also, please include some salient points from the video for when (not if) the link goes dead.

FYI, a part failure is not a mishap.  A part failure may lead to a mishap, but they are distinctly different things.  (like if your car stereo stopped working, that isn't an accident, but if you are fiddling with it while driving and smack into a tree that would be an accident.)

The airlift to Israel was Operation Nickel Grass, which should help your research.


text:
Could an airliner pilot successfully exit alone from a controlled ocean ditching?
MH370's 777 disappeared into the Indian Ocean, the investigation positing a possibility of a pilot self-hijacking the plane and flying until resource exhaustion, then gliding into a "controlled" ocean crash; perhaps why so few pieces of wreckage have ever been found.
Theoretically, if a pilot in this scenario had wanted to be picked up safely (intact), would it be technically feasible, e.g., would a pilot be able to safely exit an airliner like this alone in the water by him/herself, etc.?
Note: I'm not suggesting this occurred, nor do I think such. Merely wondering if this would be mechanically/operationally possible, as I've imagined this understandably being an involved and time sensitive process that was perhaps never designed to be done by one person alone.

See also https://en.wikipedia.org/wiki/Water_landing#Passenger_airplane_water_ditchings  for more examples of "ditching" (=controlled water crash).

I think you are confusing safely with successfully. Ditching is inherently unsafe.

Even in ideal conditions, a planned, controlled ditch of a 777 in the Indian Ocean is not likely to be successful.  The chance of hitting a wave, or just impacting the water at the less-than-perfect angle and having the entire plane break up catastrophically is very high.   If you're suggesting this was part of a DB Cooper-style plan to survive the ditching and sail away like James Bond, then it was a very stupid plan.

"the investigation positing a possibility of a pilot self-hijacking" it would be good to remove this statement or to link to the paragraph which proves it, to me it's inexact. The report didn't find any mental health problem for the crew members. The only substantial findings are the ALERFA failure and the known part of the flight path couldn't be flown by the autopilot alone, but the flight path diversion reason is unknown. Source. I rarely downvote questions, but I do for this one.

Perhaps it would be reasonable to ask whether the pilot could exit the aircraft after a successful ditching, without a significant number of passengers also exiting, and deploying life rafts &c.  And don't those rafts carry location beacons?

@mins Your source isn't the report, it's a slideshow "media briefing" of the report, and left out pertinent data from the report(s), namely, weeks before MH370 final, the PIC ran a flight sim on his home simulator: a 777 leaving KUL, flying NW into Strait of Malacca, veering left and down into south Indian Ocean, flying past fuel exhaustion, ending shortly after a user input of alt. 4,000ft. MH370 ATSB Report, p98,99, overlayed routes/Arc7 The simulator data for this flight had been wiped from PIC's computer, but was forensically recovered by the FBI.

@mins The investigation deemed the implications of this credibly and impactfully enough that it factored into MH370's search area in the Indian Ocean.
AUS MH370 ATSB Report, p98-99;
MYS MH370 Investigation Report sec. 1.5.3_2, p27-28 (source link unreachable now);
Lastly, AUS PM Tony Abbott: [paraphrased] "[It was understood at the highest levels amongst high-ranking Malaysian government and top-level officials a belief that the veteran PIC deliberately downed the jet.]"
Associated Press

@abelenky Thanks, useful to know. I wasn't suggesting that. Just wondering the feasibility of something like this even being mechanically/operationally possible.

What I see is you're not yet able to sustain your statement by a document. The document I linked is from the investigation agency and as a value. What you do is citing a government member who lacks knowledge in investigation, this is unfair, particularly since this declaration was contradicted in the same article: "In response, Malaysia’s former prime minister and police chief said there was no conclusive proof of pilot suicide" a detail you're ignoring deliberately. I'm sad to see such methods have found a way to here.

@mins Did you not read my comments? I linked to the ATSB report which states this re: the PIC's home simulator, even stating that this data was enough that it factored into determing the search areas of ocean floor to scan for MH370. You linked to a media briefing. I linked to an official gov MH370 investigation report. I tried linking Malaysia's too, but they've apparently taken it down from their MOT site. Of course there's no "conclusive proof" -- there's no conclusive proof about anything at this point beyond MH370 went missing --  nor did I ever state such.

would a pilot be able to safely exit an airliner like this alone in the water by him/herself

Assuming there had been no breakup and the pilot just want to exit the cockpit without ever entering the cabin then yes, the 777 includes an emergency cockpit exit rope (with accompanying exit hatch) as shown in this video:

Not sure why you need the rope (water is relatively soft at that height) , the bigger point is that the window is openable and can be used for egress.

@RonBeyer yes, that was sort of implied but I made it more explicit

Because the rope's in the video, @RonBeyer, and this particular plane is on the ground. ;)

…getting from the cockpit to the middle of the ocean is where the hard part begins.

Very interesting, thanks. Didn't even know this was a vector of possibility. I was picturing a time sensitive and potentially involved scenario that perhaps was never designed to be completable by one person alone.

@Coldblackice I suspect you'll find any emergency exit on any aircraft must be operable by a single person for somewhat obvious reasons

@Jamiec On the ground, sure. But in open ocean with not just an element of rising water, but complicated by a rolling sea state + inward water pressure perhaps preventing doors being opened (e.g. might a sequence be necessary to relieve pressure?), a potentially inoperable cockpit door, along with being unversed in piloting and all that would be involved, I wasn't sure. I had also heard at some point about Captain Scully in the Hudson operating something from the cockpit while passenger egress was in process.

Scully investigated aliens, Sully landed on the hudson ;)

@Jamiec LOL. I'll leave it, well played.


text:
In aircraft reliability monitoring analysis, why is the calculation of defect rate per 1000 FH?
In aircraft reliability monitoring analysis when we calculate the alert level, why is the calculation of defect rate per 1000 FH?

When calculating a rate, you have to decide what time unit you use as a basis.
For reliability monitoring, using wall clock time would not make sense, since most defects are caused by use of the aircraft, not degradation of materials over time.
Therefore flight time is more appropriate than wall clock time. Using a basis of 1 flight hour would result in very low numbers for the defect rate. Multiplying those numbers by 1000 gives a bigger number, easier to work with (fewer 0s after the decimal separator).
It must be noted that systems do also degrade over time when they are not flown. Temperature cycles during day and night causing expansion and retraction of materials, and humidity causing corrosion and evaporation of oil components in lubricants are some of the mechanisms that will cause defects over time but they are not driven by the number of flight hours.
When the defect rate is expressed in flight hours, some assumptions need to be made on the utilisation rate of the aircraft, in order to take these calendar time effects into account. This will result in higher MTBUR/MTBF values for aircraft that fly a lot (e.g. airline use) vs lower values for infrequently used aircraft (e.g. business aircraft).

I agree with everything you said. Despite the fact MTBUR/MTBF are measure in flying hours, you can't ignore non-flying hours when it comes to avionics. Just sitting on the ramp with daily temperature swings and humidity/condensation effects has a detriment on avionics. When I worked for one avionics supplier, we had separate reliability rates for the same components in aircraft in scheduled service (200-300 FH/month) and another for business aircraft (200-300 FH/year). Reliability (MTBUR/MTBF) in business aircraft was typically half of that obtained in scheduled service.

Very interesing comment @Gerry, thank you! I might try and incorporate some of that into the answer if you don't mind.

Believe me big dollar corporate airplanes don't spend any time outside when inactive.  They're pampered playthings. Low utilization IS a problem however, even kept in a heated hangar, because things both mechanical and electronic don't like to sit. In RJ land, you have corporate versions of the same airliner, and there were two separate maintenance programs each with its own analysis foundation. The bizjet program was the special Low Utilization program, where you would have calendar limits to take effect if the hours level was insufficient over some period, to account for the sitting around.

Of course @JohnK and Gerry service intervals on cars work in a similar way - maintenance that happens every year or 20000 miles, for example.  And part of this is the effect of prolonged storage on components, especially soft parts like seals sticking or deforming subtly.

Another common measures is cycles (flights), i.e. from takeoff to landing. This is especially the case for pressure-relate fatigue defects. This is especially an issue for carriers that operate short routes, e.g. inter-island flights in Hawaii or Indonesia.

No problem using my input. That's why I gave it. The biggest challenge with the data is the lower you go in the market, the harder it is to get good data. Between warranties and spares contracts, the airlines provide the flight hour data as it can save them money. Having accurate data on failure rates is used to determine how many spares to stock. When you get away from airlines and big fleet operators, the data isn't always available or reported. And most manufacturers don't willingly share the results except with their customers.


text:
How are large cargo aircraft loaded at airports?
Passenger aircraft are accessed at gates, or using buses. While they are parked waiting for passengers to board, the area they use is billed by the airport.
I was wondering what is the procedure for loading large cargo aircraft, whose payload must be moved slowly, using relatively complex equipment, and fastened to the airframe carefully.

Source
This takes time and if the area used is also billed, the cost could also climb a lot.

Do shipping companies have specific reserved areas to do that? Are these areas specifically reinforced?
What kind of fees are paid to the airport?

@Trevor Swallowing it or vomiting it out?

They will be loaded/unloaded on the ramp somewhere,
In the case of a facility like the one UPS owns in Louisville KY. they will have a large amount of ramp space in and around the facility which is on the field.

(source)
The aircraft will pull to the facility as they would a gate and be loaded there

(source)
In the case of just more generic cargo loading and unloading at an airport where no shipper has a facility the airport authority or FBO may have a facility set aside for cargo like the one at JFK. You can find a full list of the airlines/operators who have facilities at JFK here as an example. You can find a full map of the JFK cargo facilities here.
Keep in mind that some cargo will go on passenger planes and may be loaded at the gate. Along with everything else. In this case the cargo will be accepted and sorted (most likely at one of the above example buildings) and then towed over to the aircraft.
Airport fees here in the states are often charged by weight so the fees to the field will be judged on that. The fees for the cargo operations will most likely depend on what you need done such as loading/unloading, storage, customs, refrigeration, live stock services etc. I dont see any explicit prices listed but here is another one of JFK's cargo handlers CAS, I would assume you could contact them if you wanted some pricing on a given transaction.
I would not think the reinforcement is any different than anywhere else, a fully loaded aircraft be it cargo or people is the same weight.

While Louisville (UPS) and Memphis (FedEx) are the extreme cases, almost all major airports have one or more dedicated cargo terminals. In some metro areas with multiple airports, the bulk of the cargo ops are at the #2 or #3 airport.


text:
Do airline pilots practice stalls in actual aircraft?
PPL pilots are taught stall recovery by experiencing it first hand with an instructor.
Do airline pilots intentionally stall an aircraft during training? Or is it all simulator practice because it's too risky?

I don't think this is worth an answer; but I thought I'd put my two cents in. I grew up literally on a runway; and (sometimes tragic) avionic stories were hard to miss. My understanding is any type of stall, esp. such as a tail spin, is something no sane pilot would want to intentionally engage in actual flight.

@MotokoKusanagi in small aircrafts, stall (and spin, depending on which part of the world you're in) are mandatory during training. Not to mention, stalling and spinning can be so much fun!

In 727 and 747-100/200 aircraft and their simulators for the two airlines I flew those aircraft for up to my retirement in 1999, all stall training was done in simulators, never in the actual aircraft.
Stall training in the sim consisted of slowing (or otherwise loading up the wing) until the stick shaker started. Recovery was accomplished by unloading the wing and then adding power in that order. Whether unloading the wing was accomplished by just relaxing back pressure or by positive forward movement of the control column (or by rolling out of a bank if you were in one) was a judgement call.
Typically the sim instructor wanted a significant stick shaker warning, not just a quick blip that you immediately stopped. Also, it was considered bad form if, once you stopped the stick shaker, it started again. Obviously that meant you had loaded up the wing again and were moving toward a secondary stall, which was a definite no-no. As I remember, that was more likely to happen if you made the mistake of leading with power rather than first reducing the angle of attack.
Every once in awhile someone would want to play a bit and see how the sim reacted to a full stall. As I remember, the sim would just bounce around with a very high sink rate. I never felt its response to a full stall was at all representative of what the actual airplane would do.
I experienced the stick shaker in flight in a 747 three times that I remember: once during a test flight in which that was part of the testing, once with a check airman who liked to play, and once on the line.
The instance on the line was when I was still an f.o., and it was the captain's leg. He had extended the speed brakes for the descent. When he brought the power up for the final approach, he forgot about the speed brakes. The stick shaker came on immediately. He realized what he had done, and retracted them, and the stick shaker stopped.

My conclusion is you never experienced a real stall, not even in the simulator. The stick shaker comes on before serious stalling starts, and I think some accidents could have been avoided had the crew actually experienced how a stall feels (AF447, Birgenair 301, XL888T come to mind). Remember, if some sensors malfunction, the stick shaker might never activate, and you need to fly by the seat of your pants. I have made it mandatory for myself to stall every small aircraft I ever flew at different altitudes. I have even spun most of them for 3 turns or more, even an ASH-25.

@PeterKämpf You're correct in that I never experienced a real stall in a 727 or a 747, and I don't think the sims of my time accurately did a stall even when we kept the control column all the way back and let it buck. In light aircraft I've done a lot of spins. I actually found them enjoyable, although a Cessna 150 in a spin would sometimes scare people as it would really wind up after about a turn and a half if you held it in the spin. Actually, I took a lot of criticism from insisting that my private pilot students experience spins even though it wasn't required for a PPL.

@PeterKämpf Ran out of room, but I wanted to say that the airplane that I found was the most fun to spin was a J-3 on floats. The best way to do it was with the door open. It was a very slow motion spin with the nose way down and no tendency for the airspeed to increase.

We can always expect a great answer about airliners from Terry (-:

I wholeheartedly agree, every student pilot should experience spins, ideally in several different aircraft and for several turns so he/she sees what happens after the incipient spin phase. I had instructors who would spin just a half turn and then end the spin before it had fully developed. I trained spinning on slow days in gliders, when the weather was't good enough for cross-country flying and I had to kill altitude somehow. Yes, it is fun when you know what you do. Interesting observation on the J-3: I guess the added drag of the floats made the J-3 so enjoyable to spin.

Is stick shaker simulating behavior of stick in manually/hydraulically controlled planes under stall?

@PTwr The stick shakers in 747-100/200 aircraft are identical to those in the simulators for those aircraft. In the case of the aircraft, they are actuated when sensors on the aircraft indicate you are approaching a stall, although they go off well before an actual stall. I forget what the margin of safety is. In simulators they are of course, set off by the computer controlling the sim. The feel and the sound is identical since they are the same physical units. Take a look at https://en.wikipedia.org/wiki/Stick_shaker, especially the last sentence.

Usually, training is done in a simulator. Not only are the training maneuvers dangerous, but just from an economic perspective, the time in a simulator is cheaper than putting time on a real aircraft, especially for larger types.
Also, stalls are not always covered in regular training for airline pilots. Simulators do not always accurately model a plane's behavior in this situation. When properly flown, airliners should not be in danger of stalling. There are also numerous warnings, and the Airbus fly-by-wire system has an alpha floor protection feature that will automatically increase the engine power if the aircraft gets close to stalling.
However, accidents have shown that even an Airbus can stall, and pilot error has led to multiple cases of airliners stalling and crashing. The result is that pilot training is being changed to include better training for these situations. This takes time though and whether pilots currently get better training depends on the airline.

Yes, I remember reading accident investigation reports where the flight crew were under the impression that alpha prot was active when, in fact, it wasn't. Alpha prot is inactive during some modes of flight, isn't it? Or in case of certain types of consistency check failures is alpha prot disabled? I seem to recall.

@curious_cat yes, alpha protection is not always available, see this question which addresses one such case.


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Why there is no airport IATA code XXX?
It seems that there is no XXX IATA code: from Wikipedia, XVL (Vinh Long, Vietnam) is followed by XYA (Yandina, Solomon Islands). There is a source claiming that XXX used to refer to Mena Intermountain Municipal Airport, but from Wikipedia this place seems (rather strangely) to have no IATA code at all (and a source for this claim is given).
What are the reasons for not having the XXX IATA code? Is this a reserved combination? Has it belonged to the Mena Airport in the past, and if so, why has it been deregistered on October 21, 2014, as the source claims?

There are plenty of three-letter combinations that are not IATA airport codes. Why do you think XXX might be special?

I often refer to McCarren International Airport as XXX.

XXX looks like a placeholder.

Based on the IATA site Pondlife linked in his answer, DDD, EEE, FFF, III, JJJ, NNN, OOO, QQQ, VVV, WWW, and ZZZ aren't currently assigned, so there's nothing special about 3-of-the-same-letter combinations being used, either. In all, there are 17,576 available 3 letter combinations, so it's not surprising that they haven't all been assigned.

Also, if you look at the "Overview" panel of information at your source that claims it used to belong to Mena, you'll see that the end-date of the information is the day before the start date of the information. That's likely an indicator of invalid data.

They're saving it for when the Playboy mansion gets its own airport.

It looks to me like the source site you quoted is unreliable or at least not current, e.g. it gives results for codes QQQ and ZZZ too, but they haven't been assigned by IATA. The actual IATA code for Mena (ICAO: KMEZ) seems to be MZX.
Anyway, there's no particular reason why XXX, ZZZ or any other specific combination should be assigned; they just haven't been used yet. There's also no reason why IATA should assign a code to every airport: the US alone has over 5,000 public airports but only 500 or so have air carrier service.

If they're smart, XXX will never be assigned.  It's an obvious placeholder for "no code", so there are probably a lot of systems and data out there that will get confused if it ever enters use (see: the experience of people with "NO PLATE" as their vanity license plate).

@Mark Ah, the classic 'NULL' == NULL effect.


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How do tugs push back the Antonov 225?
How do tugs push back aircraft with 2 nose gears such as the Antonov 225?

https://www.youtube.com/watch?v=YiWLOPKNrsI looks like a regular tug.  I wonder if the struts are geared to turn together.

Quite simple ― use a (special) towbar! Aircraft with such unique front wheels (like the Antonov An-225 Mriya and Lockheed C-5 Galaxy) carry their own towbar around, which is then attached to the tugs for movement.
For example, here is the Galaxy's towbar:

From left to right: 68th Airlift Squadon loadmasters, Senior Airman Katy Mackey, Master Sgt. Kevin Foerster, Senior Master Sgt. Dustin Burleson, Airman 1st Class Brandon Stone, and Master Sgt. Alfonso Cervantes unload an aircraft tow bar off C-5A Galaxy upon arrival to Cairns, Australia on May 5, 2012. The tow bar was used airport officials to move the Air Force's largest transport aircraft in place to load the U.S. Coast Guard's HH-65C Dolphin helicopter. (U.S. Air Force Photo/Maj. Tim Wade)
And here's that of Mriya:

AN-225 towbar being removed from aircraft; screen grab from this youtube video.
And here's a Galaxy with a towbar:

Troops from the 439th Maintenance Squadron prepare to tow a C-5 Galaxy into Westover's Regional Isochronal dock, May 22, 2013, to test the newly-constructed mobile tail enclosure. Crews broke ground April 1, 2012, for the $5 million MTE, is a moveable structure on rails that will protect maintenance troops from harsh New England weather. The MTE is the largest structure of its kind in the Air Force. (U.S. Air Force photo/SrA Kelly Galloway)
This video shows Mriya's towbar in use.

What happens once the a/c has been towed and is ready for taxi before takeoff? I guess they open the cargo bay again to take the towbar onboard, is this correct? Thanks.

With all the spare and extra parts you think that inside the antonov there is another one hidden...

I don't think the comparison with the C-5 is actually helpful. The C-5 has just one pivoting nosegear, so its towbar isn't conceptually any different from those used on standard commercial aircraft. But the An-225 (like the B-52) has two separate nosegears on different pivots. How do you attach a towbar to that? From the video, it seems to be Y-shaped but how can it turn if it's attached to both gears?

@PlasmaHH You're suggesting that the plane's name "Mriya" is actually a contraction of "matryoshka"?

@codeaviator Yes. That's the procedure. after pushback, the nose is opened and the towbar is taken inside. I think incase of An 124, some assembly/disassembly is involved as well.

@DavidRicherby It's not exactly 'Y' shaped. More like three parallel rods with two swiveling joints, You can see more clearly in this image

@aeroalias Aha! You should definitely add that to your answer.

It is a half hour operation at the best. That's why these aircraft are usually parked away from other aircraft as they take longer to get moving.
The aircraft will usually carry its own towbar. Unlike scheduled flights where it makes sense to have your towbars positioned at the airports you operate to, for the type of flying the AN-225 does (unscheduled) it is not practical as these things cost a fair bit of money.
On the Antonov, a tow-bar is usually carried in the fwd-most position of the cargo hold. It is offloaded and the push commenced. Once the aircraft is positioned on the taxiway to the point where it can commence movement under its own engine power, the towbar is disconnected and the nose-cargo door is opened. The aircraft then 'kneels' on its nose-gear and the ramp lowered. The towbar is then wheeled on board and lashed down. The ramp is raised, the nose-gear resume the normal position and the cargo door closed.
A lot of airlines which operate an uncommon a/c type or operate to remote areas will usually have a towbar on board. But since it is such a hassle to pushback and then reload the towbar they will usually request a 'power-in/power-out' stand which works better for all involved. Air Koryo (North Korea) usually carries a towbar in the hold of their IL-62. I've also handled the Luftwaffe A310 which had a towbar in the aft hold. This was a particular pain as the tow-bar had to be lashed by the load-master.. so it was pushed back onto the taxiway, the pax steps and belt-loader positioned, towbar loaded and lashed by the Luftwaffe Loadmaster who then boarded the aircraft after which the steps and belt loaded removed. I suspect this was more to ensure that nobody stole the tow-bar!

I'm trying to imagine what circumstance would allow an unauthorized person to scoop up a towbar and carry it off a taxiway unchallenged...

@J... The most likely scenario is the tow-truck operator forgetting that this towbar is special and taking it back to wherever the airport keeps its towbars, like they do with all the others.

@DavidRicherby I suppose that's a loose interpertation of "to steal" ;)  I guess I was imagining ninjas or bandits or something.

@J... Even ninjas have to wear high-vis on the apron, which makes things very difficult for them.

@DavidRicherby  Well... you see my point, then!  That said, you could figure high-vis as apron camouflage... of a sort.

@J...: That would be exactly what a Ninja would do. Wear the most inconspicuous of garments. To... steal... a towbar... probably to forge swords of mystical strength out of the very special Stalinium steel... ;-)


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Why did the Junkers Ju-52 have corrugated external surfaces?
Every time I pass by Munich I have to pay a visit to the Deutsches museum, in particular to the aviation wing.
Among the other aircraft on display, there is a Junkers Ju-52. A different photo taken from a different website illustrates well what caught my attention:

Why are the external surfaces of both wing and fuselage corrugated?
Were the designers hoping to achieve some performance improvement through this choice? Are there any papers/documents about this?

(1) What year is the plane shown from?  (2) In what year and on what model did Prof Junkers first use the "corrgated" material?

@JoeBlow, #2 - read the Junkers history here link in Dave's great answer.

It was largely a structural decision. The Ford Tri-Motor which was designed to mimic many things the Junkers plane designs included, including the corrugated metal.

...all of which were constructed of aluminum alloy, which was corrugated for added stiffness, although the resulting drag reduced its overall performance.

Corrugated metal is common for roof panels and ironically, hangars, these days. You can find some info on the strength and flex properties of it when related to those topics. Here is an interesting thread on increased drag (and load) on corrugated roofs.
As for the availability of the material vs sheet aluminum I would argue that it had little effect on the design choice. Keep in mind all corrugated aluminum starts out as sheet aluminum at some point in the line so its hard to say there is more than one or either material. On top of that it takes more corrugated material to cover a specific square area than flat sheet material which would drive the price up. At that time period in aviation a lot of experimenting was going on and anything that made a plane a bit stronger or a bit faster was considered quite an achievement. Keep in mind we are coming of the tails of the fabric plane era so a design like this would have seemed revolutionary. The Ju-52/3m (the one you have pictured) came out in 1932 (work began in '28), by that time other makers were already looking at and working on smooth aluminum body planes. There is of course a large social aspect to the availability of materials at this time in history especially in Germany. I will refrain form a full history lesson here but you can read up on Junkers history here and about the man him self Hugo Junkers here which include some of his political views and his involvement (and issues with) the Nazi party. His work in all metal designs is credited with inspiring many passenger planes in the post WW1 and WW2 eras of design.

Dave and others.  Regarding this interesting question, I would truly like to know if the primary reason driving this decision was the already availability of this type of material, or whether Prof. Junkers went ahead and deliberately had made that type of material.

@JoeBlow: Duraluminium, the much stronger, copper-hardened version of aluminium, was developed between 1906 and 1909 by Alfred Wilm. Earlier zink-hardened  alloys developed by Carl Berg were used by David Schwarz and  Count Zeppelin. He needed it for his airships, and switched to duraluminium from 1914 on. Reissner and Junkers took what was available already.

Peter - thanks for that.  (1) What year is the plane shown from? (2) In what year and on what model did Prof Junkers first use the "corrgated" material?  (3) I may misunderstand you was the Duraluminium produced in the corrugated profile?  mfg

The Junkers J1 (the first, practical, all metal aircraft built) came about in 1915 and had a corrugated empennage and wing. This seems to vary based on the pictures you look at but one of the main partially surviving examples is in Canada and sports corrugated construction http://www.warrelics.eu/forum/imperial-germany-austro-hungary/one-kind-junkers-ju1-ww1-not-my-collection-yet-lol-354163/

Hi Dave.  Good one.  I guess what I'm not getting is:  did they use the corrugated-profile metal because that is what was on hand; or conversely dis they sit down and say "we should corrugate this {for strength, etc}" and then they had some produced with that profile, and then they used it?  Sorry I'm not really getting which of those two it is....  cheers!

@JoeBlow: Corrugated metal profiles were produced for almost a hundred years already. So, while I doubt that Junkers took profiles that some factory had in stock ("being on hand"), I also doubt that any sheet metal factory of the time would have raised an eyebrow at him ordering corrugated aluminium of this and that measurement. (I doubt any plane was designed around in-stock sheets.) And yes, the structural properties of corrugated metal (stiffness, resistance to material fatigue) were well-known, and non-corrugated sheets available, so it was a design decision. (Patented, actually.)

fantastic info. thanks!

@DevSolar: The Tupolev Tu-4 was a copy of the B-29. The Russians had several at hand after they had landed in Manchuria. But it was not a copy in the way the Chinese copy things today: All metal gauges, all bolts, all parts were converted to standard metric dimensions, so it is fair to say that the Tu-4 was designed for what the factories in Russia held in stock.

@PeterKämpf: There's a step between taking a design as-is and adapting a design to what is "in stock". That is adapting the design to the tooling available. Even if the sheet metal factory could probably comply, you don't want to ship an extra toolbox to every mechanic on every airfield there is just because that new bomber happened to have 3/8 inch instead of 10mm bolts.

The corrugated surfaces helped to save weight and drag, and they were readily available at the time. Today we would probably use sandwich panels for the same reasons, but 100 years ago those were not available.
Interestingly, the world's first all-metal airplane used already corrugated panels for the wing, while Junkers' first all-metal design was made from sheet steel. The aluminum panels for the wing and elevator of the Reissner-Ente were made in Junkers' factory and delivered to his colleague, Prof. Reissner, in 1912.

Reissner-Ente from 1912. Flying direction is to the right.
When the war broke out, Junkers felt he needed to contribute and started to build monoplanes with cantilever wings from 0.2mm steel sheets with corrugated panels welded below the smooth outer skin. The corrugated substructure worked much like the core in corrugated cardboard.

Junkers J-1 from 1915 (picture source)
Unsurprisingly, this lead to flyable, but very heavy aircraft. To lower the weight of his designs, Junkers reduced the skin to the corrugated panels and did away with the smooth skin on top, and he switched from steel to aluminum, a material which he initially avoided to reduce cost.
The low power of the engines of that time demanded low wing loadings, and surface friction was a minor contribution to the overall drag of aircraft of this time. Junkers monoplanes were the fastest fighters around, since they had no bracing wires. An additional benefit in the war for independence of the Baltic states during 1919 was their robustness - the fast shifting front lines made solid hangars impossible, and wooden airplanes were unusable after rain, so on many days only Junkers airplanes could take to the air.

Junkers J-9 (picture by Threecharlie)
If Junkers had wanted to reduce drag more, he would had made the landing gear retractable. But that would had added weight, just like a smooth layer on top of the corrugated one, and would had increased induced drag and had made the aircraft more expensive. The best compromise was to leave the corrugated surface exposed.
By 1932, when the Ju-52 flew first, this technique was already past its prime: Engine performance, construction techniques and wing loading had improved to a point that the better solution was to rivet stiffeners on the inside of a load-carrying skin. Junkers airplanes were very innovative first, but once the company had found a good way of producing robust, low-cost aircraft, it stuck to what it knew. However, Junkers' concept of a steel or aluminum truss plus the corrugated skin was heavier than the smooth monocoque skin which we still use on today's airplanes, and once aerodynamic drag could be reduced to a point where the drag increase due to the larger wetted surface of the corrugated skin could not be overlooked, even Junkers switched over. The Ju-52 was the last (and most successful) of the traditional Junkers aircraft, and the next one, the Ju-86, used the more expensive, but lighter monocoque design. Note that it had a retractable landing gear, but kept the Junkers Doppelflügel (the offset flaps and ailerons).

Ju-86 airliner of South African Airways (picture by Etienne du Plessis / Flickr.com)

Shouldn't that be “lighter semi-monocoque design”? I believe monocoque means all load is carried by skin (which was the case in Ju-52) while proper name for skin strengthened with longerons is semimonocoque.

@JanHudec: No, the traditional Junkers airplanes had an internal truss, and the corrugated skin was only a cover. Look at the windows on the side of the Ju-52: Some have a corner cut off: This is where a strut runs below the skin. Also the wing had a truss of 6 beams to carry the bending loads. Therefore, you cannot give a precise airfoil shape for Junkers airplanes: Each one had its small individual differences, depending on the way the workers bent the skin around the truss. The skin did, however, carry the chordwise loads, but this is far from a monocoque design.

The corrugated skins on the JU-52 are a strengthening/stiffening measure: Corrugated skins are less prone to bending when loaded along the corrugation (the same reason we use corrugated boxes for shipping).
While there are likely some aerodynamic penalties as a result of this, small corrugations could be within the boundary layer and the overall trade-off between weight (to brace and stiffen the skin internally) versus aerodynamics may be favorable in some designs.
The use of corrugated aluminum skins is not exclusive to the JU-52: the Ford Trimotor also used corrugated skin.
In modern designs the flight control surfaces of Piper's PA-28 family of aircraft are also corrugated - though far less dramatically, with stamped indentations to provide stiffness in lieu of internal bracing:

Short answer: To stiffen the skin in the direction of the corrugations, also the direction of flight, without adding internal structure or assembling multiple pieces that would increase weight.
Flat metal sheet was rolled to profile and bent to 3 dimensional form. The corrugations held the form along their length. Flat sheet would have required ribs, stringers or other formers to hold the shape. Corrugations have material in shear in the depth of one dimension, as well as across the length and width of the sheet.
This technique was used in other contemporary aircraft as well: The 1930s Polish PZL-7..11..24 family of fighters had corrugated skin on wings and tail surfaces, but not the large, rounded corrugations Junkers used.  Pulawski's designs made use of the Wibault-patented all metal construction that was licensed to build Wibault 7s and 72s in Poland. Vickers also licensed Wibault's patents and their US patent shows and explains how a corrugated skin with smaller corrugations works.
The A-11/YF-12/SR-71 family have corrugated skin in their wings. In their case, the corrugation allows the whole air frame to expand and contract with heating and cooling. As with Junkers, PZL, Piper, etc, Lockheed's corrugations are chordwise, stiffening the skin fore and aft.
Some post-WWII designs had a sandwich of corrugated inner skin and smooth outer skin, like Junker's early steel-skin airplanes.  Inspection/maintenance/corrosion protection must require focused attention and cost more in later years. But rolling and laminating constant gauge sheet has to cost less than integrally machined skins...

Another post-WWII design with a sandwich skin is the Grumman American AA1 and AA5 family, which have  "honeycomb sandwich" structural elements. Related patents here

If you look up "monocoque"(external supported) structures, you will learn more about why the corrugated metal was used. It has extremely high "shear" strength. If you look at the PA-28 piper's horizontal stabilizer center panel with its corrugations, if that same piece were to be made of standard aluminum, it would bend if you pressed your hand from the top center to the bottom.

Monocoque is structure that is not externally (nor internally) supported.